Day of the Moon is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.) I, II, III — Choose a creature card name, then goad all creatures with a name chosen for this enchantment. (Until your next turn, they attack each combat if able and attack a player other than you if able.)